如何在创建 FOR 循环的 POSTGRESQL 中创建存储过程？

Question

我正在研究如何在 POSTGRESQL 中创建触发器和存储过程，我的任务是更新 table ALBUM 中名为 num_long_title_songs 的列。

需要统计table首歌曲中超过12个字符的歌曲数量，然后更新ALBUM中列的值。

我已经用 for 循环创建了下一个查询，这正是我想要的：

do $$
begin
    FOR i IN 1..100 LOOP
    UPDATE ALBUM
    SET  num_long_title_songs =(SELECT count(s.title)
                                FROM ALBUM a,SONG s
                                WHERE a.id_album=s.id_album
                                AND LENGTH(s.title) > 12
                                AND a.id_album=i
                                GROUP BY a.id_album
                                ORDER BY a.id_album)
    WHERE id_album IN (SELECT a.id_album
                                FROM ALBUM a,SONG s
                                WHERE a.id_album=s.id_album
                                AND LENGTH(s.title) > 12
                                AND a.id_album=i
                                GROUP BY a.id_album
                                ORDER BY a.id_album);
    -- i will take on the values 1,2,3,4,5,6,7,8,9,10 within the loop
    END LOOP;
END; $$

问题是我需要创建一个存储过程才能创建触发器。我尝试将其放入 CREATE FUNCTION 结构中，但我无法创建它...您能帮我了解如何将此 'for' 循环放入函数中吗？

Answer 1

如果要更新 table ALBUM 中的现有行，只需运行以下 UPDATE 语句：

UPDATE ALBUM a
   SET num_long_title_songs = s.total
FROM ( SELECT s.id_album
            , count(s.title) AS total
         FROM SONG s
        WHERE LENGTH(s.title) > 12
        GROUP BY s.id_album
     ) AS s
WHERE a.id_album=s.id_album
  AND a.num_long_title_songs <> s.total ;

如果要在tableALBUM中插入或更新行时自动更新num_long_title_songs字段[=29] =] SONG, 那么你需要一个 trigger function :

CREATE OR REPLACE FUNCTION update_num_long_title_songs ()
RETURNS TRIGGER LANGUAGE plpgsql AS
$$
BEGIN
    UPDATE ALBUM a
       SET num_long_title_songs = s.total
    FROM ( SELECT s.id_album
                , count(s.title) AS total
             FROM SONG s
            WHERE LENGTH(s.title) > 12
              AND s.id_album = NEW.id_album
         ) AS s
    WHERE a.id_album=s.id_album
      AND a.num_long_title_songs <> s.total ;
END ;
$$ ;
    
CREATE TRIGGER after_insert_update_SONG AFTER INSERT OR UPDATE OF title ON SONG
FOR EACH ROW EXECUTE FUNCTION update_num_long_title_songs () ;

AFTER 很重要，以便考虑在 table SONG 中插入或更新的新行作为 num_long_title_songs[=25 的新值=].

如何在创建 FOR 循环的 POSTGRESQL 中创建存储过程？

How to create a stored procedure in POSTGRESQL that makes a FOR loop?

sql

postgresql

for-loop

stored-procedures

triggers